JP2023506442A - Method for manufacturing a flat steel product having a zinc-based metal protective layer and a phosphating layer produced on the surface of the metal protective layer, and a flat steel product of this type - Google Patents

Abstract

The present invention makes it possible, in the production of flat steel products with a Zn-based protective layer, to phosphate the flat steel products in a short time. For this purpose, according to the invention, at least the following method steps are carried out in a continuous process: providing a flat steel product coated on at least one side with a plating coating; at least partially removing by wetting over a wetting period of 60 seconds, the group "sulfuric acid, sulfurous acid, hydrochloric acid, phosphoric acid, phosphonic acid, nitric acid, formic acid, oxalic acid, acetic acid, citric acid, malic acid, c) optionally rinsing the surface of the metal protective layer wetted with the acidic solution with an aqueous rinsing solution; d) applying an activating aqueous solution. activating the surface of the metal protective layer by applying it to the surface of the metal protective layer; e) activating the surface of the metal protective layer by applying a phosphating aqueous solution to the activated surface of the metal protective layer; phosphating.

Description

The present invention relates to a method of manufacturing flat steel products having a protective zinc-based metal layer and a phosphating layer produced on the surface of the protective metal layer.

The invention further relates to flat steel products having a protective zinc-based metal layer and a phosphating layer produced on the surface of the protective metal layer.

A flat steel product is understood here as a rolled product whose length and width are each significantly greater than their thickness. Therefore, when flat steel products or "sheet metal products" are referred to below, this means rolled products, such as steel strips or steel plates, from which blanks or sheet metal blanks are separated for the production of vehicle body components, for example.

A "formed sheet metal part" or "sheet metal component" is made from such a flat steel or sheet metal product, and the terms "formed sheet metal part" and "sheet metal component" are used interchangeably herein.

The terms "phosphating layer", "phosphate layer", "phosphate crystal layer" and "phosphate coating" should also be understood synonymously below.

As used herein, the term "phosphorus crystals" refers to all crystals formed from phosphorus-containing compounds. These include, in particular, zinc phosphate crystals formed during the phosphating of the Zn coating.

"Protective zinc-based metal layer," "Zn coating" or "Zn protective layer" is used herein in the technical sense of pure zinc, or a Zn alloy, in particular a Zn-Al alloy, a Zn-Mg alloy or a Zn - used to refer to all protective layers made of Mg-Al alloy.

A protective zinc-based metal layer is applied to the steel substrate of each flat bar product as protection against corrosion.

The production of phosphate layers on flat steel products with so-called "ZM coatings" is of particular importance for the application of the method according to the invention described here.

Published by the Steel Institute VDEh, Dusseldorf, URL https://www. stahl-online. de/wp-content/uploads/2013/08/ZM-Coatings-for-Automotive-Industry. Metallic Zn-Mg-coating flat steel products of the type in question here, as described in detail in the brochure "ZINC-MAGNESIUM-ALUMINIUM COATINGS FOR AUTOMOTIVE INDUSTRY" First Edition 2013 downloadable in pdf The Al coating typically contains up to 8 wt.% Mg and Al in total. Different phases such as Zn, MgZn2, Al-rich Zn are present in such a protective layer, which respectively contribute to the protective effect of the protective coating, which is also called "ZM protective coating" or "ZM coating" in technical terminology and text. . The Al content typically varies from 0.3 to 5 wt%, while the Mg content is typically 0.3 to 3 wt%.

Optimized protective effect achieved by special distribution of Zn-, Mg- and Al-containing phases in the protective layer can minimize layer thickness while simultaneously maximizing protection against corrosion . This not only contributes to improved molding behavior, but also saves the resources needed to provide corrosion protection. This is due to the numerous applications for ZM-coated flat steel products, for example in the field of vehicle body manufacturing, and the ZM-coated metal sheets used as starting products to be turned into suitable components with a high degree of formability. Open equivalent uses to be molded.

The phosphating layer produced on the Zn-coated flat steel product contributes to protection against corrosion and is applied to flat steel products with a phosphating layer or components formed from such flat steel products. Improves adhesion of paint coatings.

Furthermore, in the case of flat steel products with a Zn coating produced by electrolytic deposition, a phosphating layer applied to the Zn coating may be used to shape the flat steel products into sheet metal parts, such as those required for the manufacture of automobile bodies. It is also used as a forming aid when forming into Here, phosphating ensures improved formability because flat steel products with phosphating on a protective metal layer leave less wear on the forming tools and exhibit improved sliding behavior. is.

General procedures for phosphating steel products coated with alloy layers are described, for example, in EP 0 454 211 B1, the specialist book "Industrial Powder Coating-Basics-Methods-Practical Use" by Judith Pietschmann, 4th Ed. , Wiesbaden, Springer Vieweg, 2013, and German Patent No. 3734596A1. The method described therein consists of a series of work steps "removing product residues and oxides etc. from the surface of the steel product using alkaline or acid cleaners", "rinsing the surface of the cleaned steel product and a process for activating the surface of rinsed steel products.

During phosphating, zinc from the protective metal layer is converted to zinc phosphate in a redox reaction with the formation of hydrogen gas, zinc phosphate is formed directly on the surface of the flat steel product coating, thus , is joined to said surface in a particularly stable manner.

Conventionally, phosphating layers are produced in a two-step process. In the first step of this process, the surface is activated by applying so-called activated particles to the flat steel product by contact with a suitable dispersion. The activated particles are used as crystal nuclei for the zinc phosphate crystals produced in the next working step, with the aim of providing smaller, denser crystals.

In the second step of conventional phosphating, a phosphating solution (consisting inter alia of phosphoric acid, water and zinc) of near-solution equilibrium is associated so that the zinc phosphate crystals can grow separately. Make contact with the surface of the protective coating of the flat bar product. When the phosphoric acid solution contacts the zinc surface, zinc dissolves from the surface of the Zn-coated flat steel product. As a result, the solubility of zinc phosphate in the phosphating solution is exceeded just above the surface of the protective Zn coating and zinc phosphate crystals are formed. The zinc phosphate crystals obtained are uniformly distributed on the surface of the protective zinc coating and follow the roughness of the steel substrate of the flat steel product.

So far, in practice it has only been possible to electrolytically phosphate surfaces with a Zn coating in a continuous process. However, the surfaces of flat steel products with a Zn coating by hot-dip coating (“hot-dip galvanizing”) could previously only be phosphated after they were formed into sheet metal components. For example, in the manufacture of automobile bodies, hot-dip galvanized metal sheets are conventionally obtained from producers of flat steel products by forming the flat steel products into components and then applying a phosphating layer to the resulting component in a dipping process. It was customary to deliver them in an unphosphated state to auto body manufacturers who provided This requires significantly longer process times than is possible during continuous phosphating of the strip material. Furthermore, with this procedure, the phosphating layer is not available as a forming aid in forming the associated sheet metal component.

In the case of ZM coatings applied by hot-dip galvanization, today only electrolytic Zn-coated flat steel products are phosphated as strip material in a continuous process because the aluminum and/or magnesium oxide layers are applied by electrolytic zinc This is because it is significantly more resistant to corrosion by phosphating solutions than Zn coatings produced by plating. The zinc oxide formed on the surface of the protective Zn layer produced by electrolytic zinc plating is dissolved very quickly by the phosphating solution. As a result, the transformation process in which metallic zinc dissolves from the surface, precipitates as zinc phosphate together with phosphate from the phosphating solution, and begins to grow on the zinc surface can begin very quickly.

In contrast, in the case of protective Zn layers applied by hot dip coating and containing Mg and/or Al, the addition of fluoride-containing components is necessary to dissolve the aluminum oxide or magnesium oxide present on the surface of the protective layer. is necessary. However, since the process of dissolving the Al or Mg oxides takes several seconds, the conversion process, which is important for the formation of the phosphating layer, can only start relatively late. Therefore, it is typically necessary to expose the relevant flat steel product to the phosphating solution for a wetting period of more than 10 seconds to dissolve the Al and/or Mg oxide layers. Such long wetting times cannot be achieved with conventional phosphating processes that are carried out continuously. Therefore, when processing hot-dip galvanized flat steel products, sheet metal components are formed from non-phosphatized flat steel products and then the resulting components are phosphated one by one using the dipping process. has hitherto only been economically feasible in industrial practice.

EP 2824213A1 discloses a method for improving the adhesion of steel sheets with a protective Zn-Mg-Al based coating, in which the protective Zn-Mg-Al based coating is applied in a continuous process. The oxide layer containing Al2O3 and MgO is then modified without pickling. For this purpose, the protective coated steel sheet is first skin-passed and then treated with an aqueous fluoride-containing composition to reduce the MgO content.

WO 99/14397 A1 discloses that a steel strip, or a steel strip galvanized on one or both sides or galvanized on one side or both sides, is treated with an acidic zinc-, magnesium- and manganese-containing phosphate at a temperature of 50-70°C. A method of phosphating by spraying or immersing the treatment solution for 2-20 seconds is described, the phosphating solution being characterized by its specific composition. However, the strip phosphating method described in WO 99/14397 A1 is not directed to flat steel products having a protective Zn-Mg-Al based layer.

Against the background of the prior art explained above, a protective metal layer is applied to the relevant flat steel product by means of a hot-dip coating (“hot-dip galvanizing”), the protective metal layer containing in particular Al and/or Mg The problem arose of providing a suitable method for the continuous phosphating of flat steel products formed from Zn alloys.

The present invention relates to the manufacture of a flat steel product having a protective zinc-based metal layer and a phosphating layer produced on the surface of the protective metal layer, at least by carrying out the working steps according to claim 1. Solved this problem.

Of course, the method steps not mentioned here and which are normally completed by a person skilled in the art in the phosphating of flat steel products of the type discussed here are, if this is required, the method according to the invention. is further performed in

Advantageous embodiments of the invention are specified in the dependent claims and are explained in detail below as is the general inventive concept.

The method according to the invention for producing a flat steel product having a protective zinc-based metal layer and a phosphating layer produced on the surface of the protective metal layer is, according to the invention, carried out in a continuous process comprising at least the following: contains the method steps of:
a) providing a flat steel product to which a protective metal layer formed from Zn, Zn--Al alloy, Zn--Mg alloy or Zn--Mg--Al alloy is applied on at least one side by hot dip coating;
b) removing at least partially the native oxide layer present on the surface of the protective metal layer by wetting the surface with an acid solution having a pH of 1-3.5 for a wetting period of 1-60 seconds from the group "sulfuric acid, sulfurous acid, hydrochloric acid, phosphoric acid, phosphonic acid, nitric acid, formic acid, oxalic acid, acetic acid, citric acid, malic acid, tartaric acid, nitrous acid or hydrofluoric acid" for acid solutions processes in which acids are used;
c) optionally rinsing the surface of the protective metal layer wet with the acidic solution with an aqueous rinsing solution;
d) activating the surface of the protective metal layer by applying an activating aqueous solution to the surface of the protective metal layer;
e) phosphating the activated surface of the protective metal layer by applying an aqueous phosphating solution to the activated surface of the protective metal layer.

The invention is thus based on flat steel products manufactured in a conventional manner and provided with a protective Zn layer in a likewise conventional manner by means of a hot dip coating, also known as "hot dip galvanizing".

Here, the invention relates to flat steel products treated according to the invention with a microcrystalline phosphate layer, such as could only be achieved in flat steel products with a Zn protective coating by electrolytic galvanizing in the prior art. Allows to generate above.

The advantage of the procedure according to the invention for producing a phosphating layer on a protective Zn-layer of a flat steel product is that this procedure allows a protective Zn-layer produced from technically pure zinc, i.e. phosphoric acid This means that a protective Zn layer in which substantially only Zn oxide is present on the surface of the protective metal layer prior to salting can also be used.

However, the method according to the present invention provides that the protective Zn layer is formed from a Zn alloy in which magnesium (Mg) and/or aluminum (Al) are present in effective amounts in addition to zinc in order to optimize the properties of the protective Zn layer. It is particularly suitable for the production of flat steel products that are Such Zn--Al, Zn--Mg or Zn--Mg--Al coatings can be produced particularly economically by hot-dip coating on steel substrates of relevant flat steel products, the surfaces of which are coated with Al and/or Mg. oxides, so that, for the reasons explained above, flat steel products coated with such Zn alloy layers as protective metal layers can be economically phosphated using conventional methods. Can not do it.

In working step b), in which the flat steel product provided in working step a) of the method according to the invention and provided with the Zn coating is treated with an acid solution before the actual phosphating step (step e)), The phosphating of flat steel products is important for the procedure according to the invention. This ensures that the native oxide layer present on the free surface of the protective Zn layer of the flat steel product provided is removed. The aim is complete removal of the oxide layer in the technical sense.

Pre-treatment with an acidic solution provided in accordance with the present invention dissolves the zinc oxide component on the surface of the Zn coating. Said pretreatment with an acidic solution can also effectively remove aluminum oxide and magnesium oxide components on the surface of the protective metal layer. After work step b) of the method according to the invention, the amount of metal oxide constituents on the surface of the Zn coating of the flat steel product, at most, follows the transformation process necessary to form the phosphating layer. is small enough to start immediately during the phosphating (step e)). Since the phosphating solution applied in the phosphating step e) is in direct contact with the non-oxide zinc on the surface of the protective metal layer, to form phosphate crystals forming the phosphating layer can start the chemical conversion process immediately.

A pretreatment with an acid solution provided according to the invention thus results in a flat steel product covered with a phosphating layer according to the invention, which is otherwise produced by electrolytic deposition of the flat steel product. It is obtained only when flat steel products with a Zn coating deposited on a steel substrate are processed.

Thus, the process according to the invention provides, in the phosphating step (step e) of the process according to the invention, a dense phosphating process within a typical duration of a continuously run phosphating process. Allows you to create layers.

Thus, the procedure according to the invention enables the production of Zn-coated, in particular Zn-Al, Zn-Mg or Zn-Mg-Al coated flat steel products economically and before they are transformed into sheet metal parts. It even allows phosphating by hot dip galvanizing in a continuous process.

In the phosphating step (operation step e) of the method according to the invention, the short treatment times made possible by the invention provide a protective Zn-based metal layer and a phosphating layer thereon, and the phosphating Flat steel products can be produced in which the phosphate crystals of the layer are particularly small and densely distributed.

A flat steel product according to the invention having a protective zinc-based metal layer and a phosphating layer produced on the surface of the protective metal layer, wherein the phosphating layer has an average crystal size of 0.5-5 μm. characterized by comprising a phosphate crystal having In this case, flat steel products according to the invention can in particular be produced using the method according to the invention.

Due to their small size, the phosphate crystals are mechanically more stable with respect to their bonding to the protective Zn layer. Additionally, the phosphate crystals of the phosphating layer made or produced according to the present invention have a greater total surface area than the coarser crystalline structure resulting from conventional batch phosphating of the component. As a result, flat steel products provided with a phosphating layer according to the invention are better for painting or gluing components formed from flat steel products according to the invention than conventionally phosphated components. have good adhesion. At the same time, the small phosphate crystals of the phosphating layer produced on the flat steel product according to the invention lead to a homogenization of the surface of the flat steel product and, associated therewith, during cold forming in the forming tool. improve behavior.

Metal oxides deposited on the surface of the Zn coating are removed according to the invention by a pretreatment with an acid solution (working step b) of the process according to the invention), so that environmentally harmful fluorides and other additives are removed. It need not be added to the phosphating solution. In addition, the content of heavy metals such as nickel and manganese in the phosphating solution can be reduced because smaller zinc phosphate crystals are formed. The procedure according to the invention is therefore also characterized by improved environmental compatibility and simpler handling.

If the component manufactured by forming a flat steel product coated with a phosphating layer according to the invention is subjected to phosphating using conventional manufacturing processes after being formed, the component phosphating compensates for damage or defects of the phosphating layer formed according to the invention on the flat steel product before it is formed into a component, thereby improving subsequent processing, in particular painting or gluing. The aim can be to achieve an optimum surface condition for For this purpose, the phosphating of the component is such that the phosphating layer is closed only on those parts of the surface of the protective metal layer which may not be covered or which are no longer optimally coated. In addition, it can be designed in a resource-saving manner.

All acids which are sufficiently water-soluble and at the same time capable of dissolving the native oxide layer on the surface of the Zn coating are suitable as acids of the acidic solution used in step b) of the process according to the invention. .

Acids from the group "sulfuric acid, sulfurous acid, hydrochloric acid, phosphoric acid, phosphonic acid, nitric acid, nitrous acid and hydrofluoric acid" are particularly suitable for this purpose. A particularly good removal of the native oxide layer can be achieved using dilute sulfuric acid as the acid solution, which is available at particularly low prices.

However, organic acids can also be used in acidic solutions as long as they are strong enough proton donors. Organic acids from the group "formic acid, oxalic acid, acetic acid, citric acid, malic acid and tartaric acid" are also suitable for the process according to the invention.

The surface of the Zn-coated flat steel product provided with the phosphating layer can be wetted with the acid solution in any suitable manner in working step a). Particularly suitable methods for applying the acid solution to the surface to be provided with the phosphating layer are the spraying, coating or dipping methods, the methods being particularly efficient when using conventional coating or spraying methods. and economical.

The length of time that the surface of the Zn coating to be phosphated must be exposed to the acid solution to remove the oxides is similarly dependent on the acid concentration of the acid solution and the temperature of the acid solution. method can be affected.

This indicates that the removal of the native oxide layer of the Zn coating according to the invention can typically be achieved within a wetting time of 1 to 60 seconds, especially 1 to 30 seconds or 1 to 15 seconds, with a wetting time of at least 5 seconds. Time has been found to be particularly advantageous in practice. Achieving wetting times of up to 10 seconds by using acids that are sufficiently aggressive and present at sufficient concentrations, by using appropriate system engineering, or by appropriate temperature control of the acid solution. can be done. In any case, the wetting time required for work step b) is so short that work step b) can be integrated with other work steps of the process according to the invention in a work sequence which is completed continuously. can be done.

A suitable range of acid concentration in the acidic solution used in accordance with the present invention can be described by the pH of the acidic solution. To achieve efficient removal of the native oxide layer without simultaneously attacking the metal surface of the Zn coating, an acidic solution with a pH of 1-3.5 is used. If the acid solution has a pH greater than 3.5, the acid solution needs to be allowed to act longer to dissolve the native oxide layer. Therefore, it is preferable to limit the pH to 2 or less so that the oxide film can be removed in a sufficiently short time. A pH value of the acid solution in the range of 1 to 1.5 has proven to be optimum.

By controlling the temperature of the acidic solution when wetting the flat steel product, the dissolution of the native oxide layer on the Zn coating of the flat steel product can be promoted. Wetting with an acid solution at temperatures between 20 and 95° C. is suitable for this. A suitable wetting temperature can be determined depending on the concentration of the acid solution and the speed at which the flat steel product passes through the section wetted by the solution, thereby resulting in the possible wetting resulting from the length of the wetting path and transport speed. The native oxide layer can be removed in time. In practice, wetting, in particular at temperatures between 20 and 80° C., has proven to be particularly suitable for this purpose.

The removal of oxides from the surface of the Zn coating of the flat steel product according to the invention may be followed by a rinsing step c), in which the surface of the protective metal layer wetted with the acid solution is cleaned of any residues of the acid solution. Rinse with an aqueous rinse solution to remove Tap water, process water or deionized water are suitable here as rinsing agents in a conventional manner.

Flat steel products pretreated by wetting with an acid solution (step b)) and optional rinsing (optional step c)) are subjected to phosphating (step e)) before phosphating (step e)). Through activation of the surface of the flat steel product provided with the treatment layer. For this purpose, an activating aqueous solution is applied to the surface of the protective metal layer provided with the phosphating layer (operation step d)). All activation solutions already used for this purpose in the prior art are suitable as agents for activation. These include, for example, powder activation based on sodium titanyl phosphate (titanyl phosphate) or liquid activation based on zinc phosphate/titanium phosphate/iron oxide.

In particular the group "titanium dioxide, titanium dioxide hydrate, dipotassium hexafluorotitanate, Hexafluorotitanic acid, titanium sulfate, titanium disulfate, titanyl sulfate, titanium sulfate oxide, titanyl chloride, titanium potassium fluoride, titanium tetrachloride, titanium tetrafluoride, titanium trichloride, titanium hydroxide, titanium nitrite, nitric acid If it contains a titanium salt selected from "titanium, potassium titanium oxalate and titanium carbide", a particularly finely crystalline phosphating layer is formed, which leads to Zn-coated flat steel products with particularly good surface properties. . Titanium salts are particularly good crystal nuclei for the crystallization of metal phosphates such as zinc phosphate. Alternatively or additionally, the activating aqueous solution may be selected from the group "oxalic acid, Zn3(PO4)2, Zn2Fe(PO4)2, Zn2Ni(PO4)2, Zn2Mn(PO4)2, Zn2Ca(PO4)2, nickel phosphate , manganese phosphate, calcium phosphate, iron phosphate, aluminum phosphate, cobalt (I) phosphate, cobalt (III) phosphate, copper, copper sulfate, copper nitrate, copper chloride, copper carbonate, copper oxide, silver, cobalt, At least one compound from nickel, Jernsted salt, lead acetate, tin chloride, tin tetrachloride, arsenic oxide, zirconium chloride, zirconium sulfate, zirconium, iron, lithium, zinc phosphate, iron phosphate, zinc oxide and iron oxide. can contain A content of 0.1 to 10 g/l of each salt or each compound has been found to be particularly practical.

If the aqueous activating solution has a starting concentration of at least 0.1 to 10 g/l, the nuclei of the phosphate crystals formed in the subsequent phosphating step are formed on the surface of the protective Zn layer within seconds. be. Activation according to the invention can be carried out particularly effectively at batch concentrations of less than 10 g/l.

Sufficient activation of the phosphorylated surface for purposes according to the present invention is ensured to be successful if the surface to be activated is exposed to the activating aqueous solution for an application time of 1-60 seconds.

The final phosphating step (working step e)) of the process according to the invention can be carried out in any known manner. Phosphating solutions known to those skilled in the art are therefore suitable for the phosphating step. For example, as already known for this purpose from the prior art, trication phosphating solutions may be particularly preferred for the formation of phosphate layers which ensure high paint adhesion or corrosion resistance. It turns out.

The phosphating of flat steel products provided and pretreated according to the present invention comprises:
5-20 g/l of phosphoric acid,
1-20 g/l of orthophosphate and/or dihydrogen phosphate,
0.5-6 g/l zinc salt,
0.5-2 g/l manganese salt,
0.5-2 g/l nickel salt,
and using an aqueous phosphating solution containing trace amounts of water and unavoidable impurities.

Here, it is advantageous if the free acid content of the phosphating solution is maintained within the range of 4-8 points and the ratio of total acid to free acid is maintained within the range of 2.5-5 points. It has been proven. Microcrystalline phosphate crystals are formed particularly reliably at free acid contents in the range of 5-7 points. The same purpose is served if the total acid to free acid ratio is maintained within the range of 2.8 to 4.5 points.

Activation (work step c)) and phosphating (work step d)) can be carried out independently of each other in a customary wet-on-wet or dry-on-wet application process. The wet-on-wet method can further increase process efficiency because an intermediate drying step can be omitted. The dry ion wet method, on the other hand, can be used particularly flexibly.

No oxide layer is formed again on the surface of the Zn coating between the removal of the native oxide layer (step a)) and the activation and phosphating of the Zn coating (steps c) and d)). A maximum of 300 seconds must elapse between the end of work step a) and the start of work step d) in order to ensure

In principle, all steels that can be coated with a protective Zn-based metal layer by using the methods of the prior art can be used as steels containing steel substrates of flat steel products to be treated according to the invention. According to a general rule, the steel preferably used according to the invention contains 0.08% by weight C, 0.45% by weight Mn, max. 0.030% P, max. S, up to 0.15 wt% Cr, up to 0.20 wt% Cu, up to 0.06 wt% Mo, up to 0.008 wt% Nb, up to 0.20 wt% Ni, and trace amounts of Consisting of Fe and unavoidable impurities, the sum of Cu, Ni, Cr and Mo should not exceed 0.50 wt% and the sum of Cr and Mo should not exceed 0.16 wt%. Steels in question include, for example, steels "CR3", "CR4" or "CR5" and "DX51" designated according to VDA material sheets VDA 239-100, high strength IF steels (e.g. DIN EN 10152, 10268, 10346 steels designated "HC180Y" according to VDA), bake hardening steels (e.g. steels designated "CR180B" and "CR210B" according to VDA material data sheets VDA 239-100), high strength steels (e.g. DIN EN 10268, 10346) and in particular high strength duplex or multiphase steels with TRIP properties. These and other possible steels are described in the brochures "Product overview: Steels for the automotive industry-product information", August 2018, version 0, and "Steel DP-W and DP-K-product information for dual-phase steels". February 2018, version 0, both published by thyssenkrupp Steel Europe AG, Duisburg, Germany.

The zinc-based coating layers provided on the relevant steel substrates and treated with the method according to the invention can have compositions known per se, as long as their main component is zinc. An example of this is the so-called "Z-coating", which consists of zinc and possibly 0.1-0.5 wt. be. Another example is the so-called "ZF-coating", which also consists of zinc and unavoidable impurities, and optionally up to 0.5 wt.% Al, but also up to 10 wt.% Fe. spread inside. A third example is the so-called "Galfan protective coating", which consists of 1-5% by weight of Al and traces of zinc and unavoidable impurities such as iron, lanthanum and cerium. The protective coatings in question are usually applied by hot dip coating.

The method according to the invention comprises a protective Zn-Mg-Al metal layer ("ZM-coating") applied to the relevant steel substrate of the flat steel product by hot-dip galvanization, the surface of which is phosphoric acid-treated by the method according to the invention. It is particularly suitable for the production of flat steel products in which a salted layer is produced. Typically such flat steel products with ZM coatings have a zinc and magnesium based coating on the steel substrate which, in addition to Zn and unavoidable impurities, contains 0.1-3 .0% by weight Mg, preferably 0.6-2.0% by weight Mg, 0.1-5.0% by weight Al, preferably 0.0-2.5% by weight Al, particularly preferably It contains 1.0-2.0% by weight of Al and optionally further alloying elements such as Fe in known amounts.

The invention is explained in more detail below with reference to embodiments.

1 represents a process sequence in a typical automotive automotive processing of a flat steel product using the method according to the invention; FIG. 1 shows an image taken with a Field Emission Scanning Electron Microscope (“FE-SEM”) of the surface of a ZM coating treated according to the present invention. 1 shows an image taken with a Field Emission Scanning Electron Microscope (“FE-SEM”) of the surface of a Z-coating treated according to the present invention. 1 shows an image taken with a field emission scanning electron microscope (“FE-SEM”) of the surface of a zinc-based coating electrolytically deposited on a sample. FIG. 4 shows a diagram reproducing the coating weights determined for the three samples. FIG. FIG. 3 shows the content of P, Ni and Mn in the phosphor coatings produced on the samples determined on three samples; FIG. 5 shows test results of adhesion behavior of five samples.

Flat steel products made of suitable steel and provided with a protective Zn-based coating are provided in the production sequence shown in Figure 1 for the production of car body components.

Prior to the first "acid rinse" step in FIG. 1, if necessary to remove residue adhering to the associated flat bar product and from previous steps in the production of the flat bar product. , a conventional degreasing process can be performed.

In the "acid rinse" step, the flat steel product is rinsed with an acidic solution to remove the native oxide layer present on the surface of the protective metal layer of the flat steel product.

The flat steel product then undergoes a "deionized water rinse" step in which the product is rinsed with deionized water to remove any residue of the previously used acidic rinse solution.

In a subsequent "activation" step, the surface of the protective coating is activated by applying an activating aqueous solution to the surface of the protective metal layer.

Then, in a "phosphating" step, the surface of the pre-activated protective layer is phosphated by applying an aqueous phosphating solution to the activated surface.

A conventional protective oil is applied to the flat steel product after phosphating (“oiling” work process) to protect it from environmental influences, and the flat steel product thus oiled is transported to the customer. (“transport to customer” work process).

The work steps completed by the customer, i.e. the processor of flat steel products: "forming/deoiling/bonding, etc.", "cleaning", "activation", "phosphating", "CDC" (CDC = "cationic 'Filler Paint'), 'Filler Paint/Topcoat' are highlighted in FIG.

To test the effectiveness of the present invention, samples E1, E2 and R were separated from conventionally produced flat steel products. The steel substrate of the flat steel product consisted in each case of the steel marketed under the designation M3A33, the composition of which is given in Table 1.

The flat steel product from which sample E1 was taken had a Zn-Al-Mg coating ("ZM coating") formed from 1.6 wt% Al, 1.2 wt% Mg and traces of Zn and unavoidable impurities. was provided in the conventional manner by hot dip coating.

The flat steel product from which sample E2 was taken was provided with a Zn coating ("Z coating") formed from 0.6 wt. .

On the other hand, the flat steel product from which sample R was taken was conventionally electrolytically coated with a protective Zn-based coating consisting entirely of zinc in the technical sense. Sample R served as a reference for testing the quality of the phosphate layers produced on samples E1 and E2 with the method according to the invention, as described below.

In a first test, flat steel product samples E1, E2 were degreased with a conventional degreasing system in a similar conventional manner using a mildly alkaline cleaning agent.

The flat steel product samples E1 and E2 were then washed with an acidic cleaning agent (URL http://www.ktl - from Henkel KGaA at wob.de/fileadmin/user_upload/Randspalte/Performanceen/Strahlen/Ridoline_124_N-GA.pdf (instructions made available for download on Jan. 9, 2006 and viewed on Oct. 30, 2019) available) was used to wet the surface of these ZM coatings by dipping or spraying the cleaner to remove the existing native oxide layer.

After this treatment, the flat steel product samples E1, E2 were conventionally rinsed with deionized water to remove any residue of the acid cleaner present on them.

For activation, 2.1 g/l of the conventionally known "Fixodine® 50CF" or "Bonderite®" was applied to the surface of the thus washed ZM coating of sample E1 and of the Z coating of sample E2. A solution containing TM M-AC 50CF' activator was sprayed at room temperature for a treatment time of 5 seconds.

Then, on the activated surface of the ZM coating of the flat steel product sample E1 and the Z coating of the sample E2, the temperature was 60° C., 2.2 g/l nickel, 2 g/l manganese, 8.6 g/l phosphorous , 2.6 g/l zinc and 13.1 g/l nitrate dissolved in water for 5 seconds. The pH of the phosphating solution was 2.55.

Flat steel product samples E1 and E2 phosphated in this way were sprayed with deionized water for 20 seconds to remove phosphating agent residues.

Finally, samples E1, E2 were dried in a drying cabinet at 70°C.

Reference sample R was treated in the same manner as the other samples, except for the pickling and rinsing performed according to the invention.

FIG. 2a shows an FE-SEM image of a section of the surface of the ZM coating of flat steel product sample E1 treated in the manner described above.

FIG. 2b shows an FE-SEM image of a section of the surface of the Z-coating of flat bar sample E2 treated in the manner described above.

FIG. 2c shows an FE-SEM image of a section of the surface of the electrolytically deposited Zn-based coating of flat steel product sample R (reference) treated in the manner described above.

Comparing Figures 2a to 2c, the process according to the invention can be used to reliably produce a fine-crystalline coating phosphate layer on protective Zn-based coatings of flat steel products produced by hot-dip coating. is possible (see Figures 2a and 2b), which can otherwise only be achieved with an electrolytically deposited Zn coating (see Figure 2c).

This result was confirmed by measuring the coating weight of the phosphate layers produced on samples E1, E2 and R using glow discharge spectroscopy (glow discharge optical emission spectroscopy, GDOS/GDOES). The coating weights of all coatings determined for samples E1, E2 and R are presented in the diagram shown in FIG. Phosphating the coating of the flat steel product samples E1 and E2 produced by hot-dip coating, prepared and performed in accordance with the present invention, removed the phosphate layer conventionally produced on the electrolytically coated reference sample R. It can be seen that this results in a coating weight that differs only slightly from the coating weight.

The percentage contents of P, Mn and Ni were also determined for the phosphate layers produced on samples E1, E2 and R. The measurements were performed using a glow discharge spectrometer "Spectruma GDA 750" (focal length 750 mm, simultaneous vacuum spectrometer equipped with a Grimm-type discharge source and capable of measurements in DC and RF modes). Measurements were made in RF mode. The device was operated with a 4 mm anode and Argon 5.0 (99.999%) gas. Typical parameters for each device for operation with a 4 mm anode were a voltage of 800 V, a current of 20 mA, a power of 16 W and a lamp pressure of 3-10 hPa. Additionally, as part of the measurement, the pre-plasma was connected upstream for 25 seconds. The results of this investigation are summarized in the attached figure as FIG. From this it follows that the phosphate layers produced according to the invention on samples E1 and E2 each coated with a fused Zn coating are technically identical to reference sample R provided with a protective Zn-based coating by electrolytic coating. It turns out that it has a composition.

In order to evaluate the improved tribological behavior achieved by the phosphor layers produced according to the present invention, samples E1, E2 and reference sample R, and two comparative samples C1, C2 were tested as "pin-on-disk" tests. Served what is known. Comparative sample C1 is a sample of flat steel product with a ZM coating, from which sample E1 was also produced, which was further coated with a phosphor layer in the method according to the invention. Comparative sample C2 was thus a sample of a flat product with a Z coating, from which sample E2 was also produced, which was further coated with a phosphor layer in the method according to the invention. Both the top and bottom sides of samples E1, C1, E2, C2, R were examined.

All samples E1, C1, E2, C2, R were lubricated with a commercial oil prior to pin-on-disk testing. This oil is the oil supplied by Fuchs Schmierstoff GmbH under the name "ANTICORIT PL 3802-39/S" which has been tried and tested for this purpose, and samples E1, C1, E2, C2 to be tested , R with a coating of 1.2 g/m ² per surface.

In the pin-on-disk test, the conical tip of the specimen is pressed against the surface of a circular disk-shaped section of the relevant sample with a normal force N, and the rotation oriented perpendicular and normal to the exposed surface of the specimen. rotated around an axis. The frictional force between the test piece and the surface of the sample blank is measured and the coefficient of friction is calculated from the determined frictional force and the normal force N. The pin-on-disc test used specimens with a cone diameter of 5 mm. The specimen consisted of a steel known as 100 Cr6 (W3) and was heated to 60°C for testing. The tip of the specimen was oriented against the test surface with a normal force N, which was 30N.

The pin-on-disk test results are summarized in Table 2. It is clear that the samples E1, E2 coated according to the invention with a phosphating layer have a more favorable coefficient of friction μ, not only in comparison with the comparative samples C1, C2, but also in comparison with the comparative sample R.

Finally, the suitability of samples E1, E2 phosphated according to the invention was investigated in comparison with non-phosphated samples C1, C2 and reference sample R.

Prior to gluing, samples E1, C1, E2, C2, R with a coating weight of 1.2 g/m ² were obtained from Fuchs Schmierstoff GmbH under the name "ANTICORIT PL 3802-39/S" for this purpose. It was lubricated with a known oil for

The adhesive used in the tests is a commercial structural adhesive known as "Betamate 120 EU", which is widely used in the manufacture of automobile bodies. The tensile shear test is based on DIN EN 1465. Five similarly treated copies of samples E1, C1, E2, C2, R were investigated to ensure representative relevance of the findings.

Breaking behavior is evaluated according to DIN EN ISO 10365. A distinction is made between three types of fracture.

- cohesive failure (abbreviated "CF") resulting in breakage of the adhesive,
- Adhesive failure (abbreviated "AF"), where the break occurs at the interface between the oxide layer and the adhesive,
and - near-substrate cohesive failure ("SCF") where the adhesive breaks near the interface between the oxide layer and the adhesive.

An adhesive bond with a higher percentage of cohesive failure "CF" that satisfies the practical requirement that the adhesive bond must be lost in the area of the adhesive itself, rather than at the interface between the surface of the component involved and the adhesive. increase in the proportion of

The results of the adhesion behavior tests are summarized in FIG. Results determined on samples in their initial state are identified by the word "AFW", whereas results determined on samples that have undergone 10 cycles of climate change testing according to DIN EN ISO 11997-B are marked with "10VDA". be.

Adhesive compatibility of samples E1, E2 phosphated according to the invention, as measured by the percentage of cohesive failure patterns, is significantly improved compared to non-phosphatized samples C1, C2 and the reference sample. I understand that.

Claims (8)

A method for manufacturing a flat steel product having a protective zinc-based metal layer and a phosphating layer produced on the surface of said protective metal layer, comprising the following method steps carried out in a continuous process:
a) providing a flat steel product to which a protective metal layer formed from Zn, Zn--Al alloy, Zn--Mg alloy or Zn--Mg--Al alloy is applied on at least one side by hot dip coating;
b) at least partially removing a native oxide layer present on said surface of said protective metal layer by wetting said surface with an acid solution having a pH of 1 to 3.5 for a wetting period of 1 to 60 seconds. removing, for the acidic solution, the group "sulfuric acid, sulfurous acid, hydrochloric acid, phosphoric acid, phosphonic acid, nitric acid, formic acid, oxalic acid, acetic acid, citric acid, malic acid, tartaric acid, nitrous acid or hydrofluoric acid is used, a process in which an acid from
c) optionally rinsing the surface of the protective metal layer wet with the acidic solution with an aqueous rinsing solution;
d) activating said surface of said protective metal layer by applying an activating aqueous solution to said surface of said protective metal layer;
e) a method comprising at least the step of phosphating said activated surface of said protective metal layer by applying an aqueous phosphating solution to said activated surface of said protective metal layer. 2. A method according to claim 1, characterized in that in working step b) the surface of the protective metal layer is wetted with the acid solution by a spraying, coating or dipping method. 3. A method according to either claim 1 or 2, characterized in that said wetting period is a maximum of 15 seconds. A method according to any of the preceding claims, characterized in that the acidic solution is heated to a wetting temperature of 20-95°C before the surface of the protective metal layer is wetted. Method according to any of the preceding claims, characterized in that in optional working step c) fully demineralized water is used as said aqueous rinsing solution. Said activating aqueous solution used in step d) belongs to the group "titanium dioxide, titanium dioxide hydrate, dipotassium hexafluorotitanate, hexafluorotitanic acid, titanium sulfate, titanium disulfate, titanyl sulfate, sulfate oxidation. Titanium, titanyl chloride, titanium fluoride potassium, titanium dioxide, titanium dioxide hydrate, dipotassium hexafluorotitanate, hexafluorotitanic acid, titanium sulfate, titanium disulfate, titanyl sulfate, titanium oxide sulfate, titanyl chloride, 0.8-25 g of at least one salt from "potassium titanium fluoride, titanium tetrachloride, titanium tetrafluoride, titanium trichloride, titanium hydroxide, titanium nitrite, titanium nitrate, potassium titanium oxide oxalate or titanium carbide" /l. The aqueous phosphating solution used in step e) is
5-20 g/l of phosphoric acid,
1-20 g/l of orthophosphate and/or dihydrogen phosphate,
0.5-6 g/l zinc salt,
0.5-2 g/l manganese salt,
0.5-2 g/l nickel salt,
and trace amounts of water and unavoidable impurities. Method according to any of the preceding claims, characterized in that at most 300 seconds elapse between the end of work step a) and the start of work step d).

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